The present invention relates to an optical-disc recording and reproducing apparatus acting as an optical information reproducing and recording apparatus which is applicable to a mini disc (MD) player, a recorder, a CD player, or the like which reproduces information from an optical disc or records information thereon for reproduction.
Tracking control in a conventional optical-disc recording and reproducing apparatus will be described with reference to FIG. 8. As shown in this figure, this optical-disc recording and reproducing apparatus is comprised of an optical disc 1 capable of at least either recording or reproduction; a spindle motor 2 for rotating the optical disc 1; an optical pickup 6 for recording/reproducing signals on or from the optical disc, the optical pickup having an objective lens 3 for irradiating the optical disc 1 with light, a tracking actuator 4 for supplying a current to a tracking actuator coil to move the objective lens 3, and a light receiving section 5 for receiving an optical spot from the optical disc 1; an optical head 7 for holding the optical pickup 6; a traverse mechanism 8 for moving the optical head 7 in a radial direction A of the optical disc 1; a traverse mechanism-controlling section 9 for controlling the traverse mechanism 8; an arithmetic section 10 for calculating a signal received by the light receiving section 5 of the optical pickup 6; a tracking error signal-generating section 11 for generating a tracking error signal based on an output signal from the arithmetic section 10; a tracking controlling section 12 for determining a gain, a frequency characteristic, and a phase characteristic required for continuous tracking on the optical disc 1 based on the signal generated by the tracking error signal-generating section 11; a tracking driving section 13 for driving the tracking actuator 4; and a controller 14 for controlling the traverse mechanism-controlling section 9 and the tracking controlling section 12.
The tracking driving section 13 drives the tracking actuator 4 to move the objective lens 3 in a radial direction B of the optical disc 1 within an internal movement range of the optical head 7 in a fashion following tracks of the optical disc 1.
The traverse mechanism-controlling section 9 controls the traverse mechanism 8 to move the entire optical head 7 in the radial direction A of the optical disc 1.
As shown in FIG. 9, the light receiving section 5 is comprised of abeam splitter (not shown) for splitting (a split line 34) the optical spot from the optical disc 1 in a direction generally in parallel with the tracks of the optical disc 1 and outputting the obtained beams, and a photodetector 15 having a plurality of light receiving elements 30 to 36 for receiving the split light. The arithmetic section 10 is comprised of an amplifier 38 for generating an optical-spot offset signal and an amplifier 39 for generating the tracking error signal. FIG. 9 represents the photodetector 15 of the optical pickup 6 and an optical spot 37 on the photodetector 15 in a pseudo manner.
A tracking control operation performed by this optical-disc recording and reproducing apparatus will be described below. While being rotated by the spindle motor 2, the optical disc 1 is irradiated with laser light for reproduction/recording which is controlled to focus on the optical disc 1. The tracking error signal generating section 11 generates the tracking error signal based on a signal received by the photodetector 15 of the light receiving section 5 of the optical pickup 6. Based on the tracking error signal, a signal having a gain, a frequency characteristic, and a phase characteristic required for continuous tracking on the optical disc 1 is supplied to the tracking actuator 4 of the optical pickup 6 through the tracking controlling section 12 and the tracking driving section 13 to perform the tracking operation.
In a tracking controlling method used by such an optical-disc recording and reproducing apparatus, if this apparatus assumes a position in which the optical disc 1 lies horizontally, the tracking driving section 13 provides no output before starting tracking control and is thus located in such a manner as to balance itself with the gravity G (generally at the center of the movement range of the tracking actuator 4). Since an electric offset or the like is provided in this position, in the above tracking conditions, the tracking operation is performed around the position in which the tracking driving section 13 balances itself with the gravity G.
In addition, if this apparatus assumes a position in which the optical disc 1 stands vertically, the tracking drive section 13 provides no output before starting tracking control and is thus located in such a manner as to balance itself with the gravity G (at a position outward or inward offset from the movement range of the tracking actuator 4). Accordingly, the movement range of the tracking actuator 4 may shift outward or inward significantly depending on the weight of the objective lens 3 or the characteristics of a member supporting the objective lens 3. Then, the tracking operation is performed for reproduction or recording around a position in which the objective lens 3 is substantially displaced. Consequently, in the worst case, signals cannot be read or information cannot be recorded accurately.
Such tracking control carried out by conventional optical-disc recording and reproducing apparatuses is disadvantageous in that the displacement of the objective lens caused by the gravity depending on the position of this apparatus cannot be corrected, thereby degrading reproduced signals.
It is an object of the present invention to provide an optical-disc recording and reproducing apparatus that realizes stable tracking control capable of correcting the displacement of the objective lens caused by the gravity depending on the position of the apparatus.
An optical-disc recording and reproducing apparatus according to the present invention comprises optical-spot offset-controlling means operating before a tracking operation to calculate an output signal from the light receiving section to detect relative displacement of an optical spot on a light receiving section in order to drive and position a tracking actuator in a manner such that the relative displacement is maintained at a fixed value.
According to the present invention, in every position of the present apparatus, displacement of the objective lens caused by the gravity depending on the position of the present apparatus can be controlled to place the object lens at a position substantially corresponding to a horizontal position of the present apparatus, thereby minimizing variations in the tracking actuator originating from the displacement of the objective lens caused by the gravity depending on the position of the present apparatus. Consequently, a movement range of the tracking actuator can be set within a range in which the tracking actuator can be stably controlled.
A first aspect of the present invention is an optical-disc recording and reproducing apparatus comprising an optical pickup having an objective lens for irradiating an optical disc with light beams, a light receiving section for receiving an optical spot from the optical disc, and a tracking actuator for moving the objective lens in a radial direction of the optical disc, the apparatus performing a tracking operation by driving the tracking actuator based on a tracking error signal obtained from an output signal from the light receiving section, wherein the optical disc recording and reproducing apparatus further comprises optical-spot offset-controlling means adapted, before the tracking operation, for calculating the output signal from the light receiving section to detect relative displacement of the optical spot on the light receiving section in order to drive and position the tracking actuator, thereby maintaining the relative displacement at a fixed value. With this configuration, in every position of the object lens, displacement of the objective lens caused by the gravity depending on the position of the present apparatus can be controlled to place the object lens at a position substantially corresponding to a horizontal position of the present apparatus, thereby minimizing variations in the tracking actuator originating from the displacement of the objective lens caused by the gravity depending on the position of the present apparatus. Consequently, a movement range of the tracking actuator can be set within a range in which the tracking actuator can be stably controlled. Thus, possible degradation of the tracking error signal induced by the displacement of the object lens can be minimized to stabilize the error signal level and balance during the tracking operation. As a result, stable tracking control can advantageously be provided.
A second aspect of the present invention is an optical-disc recording and reproducing apparatus comprising an optical pickup having an objective lens for irradiating an optical disc with light beams, a light receiving section having a plurality of light receiving elements for splitting an optical spot from the optical disc into pieces before receiving them, tracking error signal-generating means for generating a tracking error signal from output signals from the plurality of light receiving elements, a tracking driving section for driving a tracking actuator that displaces the objective lens in a radial direction of the optical disc, tracking controlling means for performing a tracking operation by driving the tracking actuator based on the tracking error signal, and optical-spot offset-controlling means adapted, before the tracking operation, for operating calculation of the output signals from the plurality of light receiving elements in order to detect relative displacement of the optical spot on the light receiving section, and driving and positioning the tracking actuator, thereby maintaining the relative displacement at a fixed value. This aspect provides effects similar to those of the first aspect of the present invention.
In addition, in the optical-disc recording and reproducing apparatus, the optical-spot offset controlling means comprises a positional signal-generating section for calculating the output signals from the plurality of light receiving elements to detect the relative displacement of the optical spot on the light receiving section, a variable-gain amplifier for varying a gain for an optical-spot offset signal from the positional signal-generating section or a fixed gain amplifier having a fixed gain for the optical-spot offset signal, and a positional signal-controlling section for varying a gain with which the tracking actuator is driven. A configuration can thus implemented by operating, before the tracking operation, calculation of an output signal from the light receiving section in order to detect relative displacement of the optical spot on the light receiving section, and driving and positioning the tracking actuator in a manner such that the relative displacement is maintained at a fixed value.
Further, in the optical-disc recording and reproducing apparatus according to the present invention, the tracking controlling means is configured to take over a low-range item of a drive value for the tracking actuator after positioning control and then perform the tracking operation by driving the tracking actuator based on the tracking error signal. In every position of the present apparatus, the displacement of the objective lens caused by the gravity depending on the position of the present apparatus can be controlled so as to place the object lens at a position substantially corresponding to a horizontal position, thereby minimizing degradation of the tracking error signal originating from the displacement of the objective lens caused by the gravity depending on the position of the present apparatus. Consequently, the error signal level and the balance during the tracking operations are stabilized so that a system capable of stable tracking control can be obtained.